Electronic flash circuits

ABSTRACT

An electronic flash device for providing artificial illumination. A main capacitor is connected between the electrodes of a discharge tube to which there is also connected an ignition transformer for bringing the tube into a state of emission. A trigger switch and a trigger capacitor are connected with the transformer for actuating the latter. By way of the trigger switch an additional capacitor is connected in series with the main capacitor so that at its initial period of emission the inter-electrode voltage of the discharge tube is augmented by the discharge from the additional capacitor.

United States Patent 1191 Tadokoro Dec. 25, 1973 [54] ELECTRONIC FLASH CIRCUITS 3,001,125 9/1961 Jensen 315/241 P x [75] Inventor: Kinya dok o, a i ap 3,115,594 12/1963 Mallory 315/241 R X [73] Assignee: Kabushiki Kaisha Sunpak, primary Examine,- A]fred L Brody Tokyo-t0, Japan Attorney-Harold D. Steinberg et a1. [22] Filed: June 16, 1971 21 Appl. No.: 153,520 1 ABSTRACT An electronic flash device for providing artificial i1- 30 Foreign A li ti priority Data lumination. A main capacitor is connected between June 23 1970 M an 45/6232. the electrodes of a discharge tube to which there is p also connected an ignition transformer for bringing [52] CL 315/241 P 315/238 315/240 the tube into a state of emission. A trigger switch and [51] Int. CL 6 41/32 a trigger capacitor are connected with the transformer of IIIIIIIIIIIII for actuating the latter Way Of the trigger SWltCh an /241 P R 41 additional capacitor is connected in series with the main capacitor so that at its initial period of emission he inter-electrode voltage of the discharge tube is [56] References Clted t augmented by the dlscharge from the addmonal ca- UNITED STATES PATENTS packer 3,697,805 10/1972 Switsen 315/240 X 2,724,792 11/1955 Nessel 315 241 P X 4 Claims, 3 Drawing Figures PATENTEU DEC 2 51975 INVENTOR AVA/m 740mm,?!)

A ORNEYS ELECTRONIC FLASH CIRCUITS BACKGROUND OF THE INVENTION The present invention relates to electonic flash devices.

As is well known, cameras are provided with electronic flash devices so that when insufficient light is available for making a proper exposure, the electronic flash device may be ignited to bring about artificial illumination suitable for making an exposure.

With devices of this type, the structure is designed to obtain a maximum amount of illumination with a minimum amount of power. The discharge tube of such devices are usually filled with xenon gas, and discharge is obtained by ionization of the gas. The amount of emission obtained from a given discharge tube depends upon such factors as the inter-electrode distance of the discharge tube, the type of gas therein, the arrangement of the electrodes, and similar factors. When a discharge tube with a relatively large inter-electrode distance is used in order to increase the amount of emission, a correspondingly higher inter-electrode voltage is required in order to bring about the effective discharge through the inter-electrode distance. It has been conventional to use for a conventional electronic flash device a power source which may take the form of a high voltage layer-built drycell, a converter means using a low voltage drycell power source, or the like. However, the requirement of a high voltage power source in order to obtain the increased emission has resulted in large dimensions and weight of the layer-built drycell, and this factor is of considerable disadvantage particularly with respect to the portability of the device. Utilizing a boosting converter also has required an undesirably long period of charging in order to achieve a predetermined charge or terminal voltage with a capacitor which must be charged and discharged to bring about the emission.

Even if it is attempted to increase the amount of momentary electrical discharge, so as to increase the amount of emission by increase of the filled gas pressure and improvement of the discharge electrode, the voltage source must be made undesirably greater as in the above cases.

. SUMMARY OF THE INVENTION It is accordingly a primary object of the present invention to provide electronic flash circuitry which will avoid the above drawbacks.

In particular, it is an object of the present invention to provide electronic flash circuitry which will enable a discharge tube to emit light equal to that which is conventionally emitted with conventional devices but which uses instead for this purpose a smaller power source.

Also, it is an object of the invention to provide electronic flash circuitry which will enable a given source of power to achieve a greater emission than has been heretofore achieved with a power source of the same magnitude.

Thus, it is an object of the present invention to provide a relatively simple electronic flash circuit which is capable of making more efficient use of the available power.

According to the invention the electronic flash device includes a discharge tube which has a pair of electrodes. A main capacitor is connected between these electrodes to regulate the inter-electrode voltage of the discharge tube. An ignition transformer is operatively connected with the discharge tube to bring the latter into a state of emission, and a trigger capacitor as well as a trigger switch are electrically connected with the transformer for actuating the latter. An additional capacitor is connected in series with the main capacitor upon closing of the trigger switch so that at its initial period of emission the inter-electrode voltage of the discharge tube has the voltage from the additional capacitor added to the voltage from the main capacitor.

BRIEF DESCRIPTION OF DRAWINGS The invention is illustrated by way of example in the accompanying drawings which form part of this application and in which:

FIG. 1 is a diagram of conventional electronic flash circuitry;

FIG. 2 is a diagram of electronic flash circuitry according to the invention; and

FIG. 3 is a diagram of electronic flash circuitry of the invention presenting an improvement over that of FIG. 2.

DESCRIPTION OF PREFERRED EMBODIMENTS Referring first to FIG. 1 which shows conventional electronic flash circuitry, this conventional structure includes a power source 1, a fixed resistor 2, and a main capacitor 3, the resistor 2 and capacitor 3 being connected in series with the source 1. An additional series circuit is provided for the discharge tube 8, a trigger capacitor 5, of relatively small capacitance, and a resistor 4. The series connected capacitor 5 and resistor 4 are connected in parallel with the terminals of the main capacitor 3. An ignition transformer 6 has its primary winding connected in parallel with the trigger capacitor 5, by closing of a trigger switch 7. Thus, the primary winding of ignition transformer 6 forms a closed-loop series circuit with the trigger capacitor 5 and the trigger switch 7. The secondary winding of the trigger transformer 6 will apply a high voltage to an ignition electrode 9 carried by a side wall of the discharge tube 8.

The main capacitor 3 is charged in accordance with its capacitance, but the emission of the discharge tube 8 takes place upon closing of the trigger switch 7 at which time the charge from the main capacitor 3 is not immediately applied to the discharge tube 8. More specifically, upon closing of the switch 7, the charge voltage of the trigger capacitor 5, of relatively small capacitance, is applied to the ignition transformer 6. A high voltage develops in the secondary winding of the trigger transformer 6, and the xenon gas which fills the discharge tube 8 undergoes ionization due to the application of the high voltage of the trigger electrode 9. As a result the inter-electrode resistance of the discharge tube 8 is sharply reduced, and then the discharge tube 8 undergoes a discharge with the charge of voltage from the main capacitor 3 as a result of this drop in resistance.

With the present invention there is an improvement in the supply of power to the discharge tube in such a way as to obtain a higher degree of ionization for the xenon gas.

Referring to FIG. 2, it will be seen that the ignition transformer 6 has its primary winding connected in series with an additional capacitor 10 which is electrically connected to the anode side of the discharge tube 8.

This discharge tube 8 is connected in parallel with the main capacitor 3, with a resistance 1 1 being inserted on the anode side. The trigger switch 7 is connected to a junction between the primary winding of the trigger transformer and the additional capacitor 10, and of course the trigger switch 7 is connected to one side of the trigger capacitor 5 of relatively small capacitance so as to short circuit the capacitor 5 when the switch 7 is closed.

Thus, with the embodiment of FIG. 2, there is a series connection between the main capacitor 3 and the additional, separate capacitor 10, this series connection being established upon closure of the switch 7 so that it becomes possible to apply temporarily the increased voltage derived from both capacitors 3 and to the discharge tube 8 during the initial period of emission thereof. As a result the gas which is filled in the interior of the discharge tube 8 is ionized by the high voltage of the transformer 6 under the application of the increased voltage, with the result that the discharge tube 8 is very easily placed in its initial state of emission with a reduced electrical resistance.

Thus, in accordance with the'invention, the charge voltage of the additional or separate capacitor 10 is used in addition to the inter-electrode voltage of the discharge tube 8 which is derived from the main capacitor 3 for the purpose of starting the emission, with the result that the power source 1 can have a relatively low output voltage in accordance with the charge terminal voltage of the capacitor 10.

While the embodiment of FIG. 2 will indeed provide an improvement over the conventional circuitry shown in FIG. 1, this embodiment of FIG. 2 has a disadvantage in that the electrical charge of the additional or separate capacitor 10 cannot be effectively utilized to the desired extent due to the leakage current resulting from the presence of the resistance 11. This disadvantage is effectively avoided by the embodiment of FIG. 3 which is identical to that of FIG. 2 except that instead of a resistance l 1 the embodiment of FIG. 3 uses a diode 12. Thus, by replacing the resistance 11 of FIG. 2 with the diode 12 of FIG. 3 the leakage current of the capacitor 10 is blocked by the diode even upon establishment of the series connection between the main capacitor 3 and the separate capacitor 10 upon closing of the trigger switch 7, so that in this way the voltages of both capacitors 3 and 10 are applied in their entirety to the discharge tube 8 and the electrical charge of the capacitor 10 is thus very effectively used for emission purposes, thus enabling a very efficient use of the additional capacitor 10 to be achieved.

Thus, with the present invention there is an improved flash device in which an emission output equal to that of a conventional flash device can be maintained while utilizing the reduced source voltage and thereby achieving a higher economy as well as increasing the ease of portability. With the improved flash device of the invention the use of a power source having a source voltage equal to that of a conventional source voltage will achieve an incaresed emission output.

With the structure of the invention the main capacitor will regulate the inter-electrode voltage of the discharge tube with the ignition transformer being used to bring the discharge tube into the range for starting the emission, and the capacitor 5 of small capacity as well as the trigger switch both serve to regulate the source voltage of the transformer. The additional capacitor l0 is inserted in a series connection with the main capacitor 3 in synchronization with or at least just prior to closing of the switch 7, and the inter-electrode voltage of the discharge tube is achieved at an initial period of its emission from the charge voltage of the main capacitor and the increased voltage which is added to the charge voltage.

Thus, as will be apparent from the above description, with the present invention the electronic flash device is greatly improved in view of the fact that an emission output at the level of a conventional flash device can be obtained with a smaller power source than that which is required by a conventioanl flash device while the use of a source voltage of the same magnitude as that which is used in a conventional flash device would effectively increase the pressure of gas filled in the discharge tube 8, and as a consequence the emission output will be increased.

In actual practice it has been found that with a discharge tube used in conventional circuitry as shown in FIG. 1, where the lower limit of the discharge voltage (voltage at the point when the discharge tube will no longer emit during the gradual dropping of the charge voltage from the main capacitor) is 200V, it is possible with the structure of the present invention to effectively replace such a discharge tube by one where the low limit of discharge voltage is V, with the embodiment of FIG. 3. It has also been found in actual practice that when the pressure of gas filled in the discharge tube employed with the embodiment of FIG. 3 is raised, so as to obtain a low limit of discharge voltage of 200V, the emission output was increased by approximately 30 percent as compared to conventional circuitry.

As is apparent from the above description and the drawings, the resistors 11 and 4 in the case of FIG. 2 and the diode l2 and the resistor 4 in the case of FIG. 3 form a means for establishing the series connection between the capacitors 3 and 10 upon closing of the trigger switch 7. It is furthermore to be noted, as shown in FIGS. 2 and 3, that the resistor 4 of this means which serves to establish the series connection between the capacitors 3 and 10 is connected between the trigger circuit 5-7 and the negative pole of the source 1. Therefore the trigger circuit 5-7 of the invention is separated from ground by the resistor 4. In order to connect the flash structure to the camera electrically, a trigger cord is extended from the switch 7 to the outside of the flashing unit and is connected to the camera. The connecting element of this cord may contact the hand of the photographer. Since the resistor 4 prevents leakage of current between the positive side of capacitor 5 and ground, the resistor 4 will prevent any danger to the photographer.

What is claimed is:

1. In an electronic flash device, a discharge tube having a pair of electrodes, a main capacitor electrically connected between said electrodes for regulating the inter-electrode voltage of said discharge tube, an ignition transformer operatively connected with said discharge tube for bringing the latter into a state of emission, a trigger switch and a trigger capacitor electrically connected with said transformer for actuating the latter to start the emission of said discharge tube, an additional capacitor to be connected by said trigger switch upon closing thereof in series with said main capacitor for providing at an initial period of emission of said discharge tube an inter-electrode voltage from said main capacitor and said additional capacitor, and means for establishing said series connection between said main capacitor and additional capacitor upon closing of said trigger switch, said trigger transformer having a primary winding forming a closed-loop series circuit with said trigger capacitor and said trigger switch which thus short-circuits said trigger capacitor across said primary winding upon closing of said trigger switch, said additional capacitor being connected in series with said primary winding with said trigger switch being connected to a junction situated between said additional capacitor and said primary winding.

2. The combination of claim 1 and wherein said trigger transformer, said trigger switch and said trigger capacitor form a trigger circuit, a power source having a positive terminal electrically connected with the anode of said discharge tube, and said power source having an opposed negative terminaL'and said, means for establishing said series connection between said main capacitor and additional capacitor including a resistor connected between said trigger circuit and negative termi nal of said power source and separating said trigger circuit from said negative terminal.

3. The combination of claim 1 and wherein said trigger transformer, trigger switch, and trigger capacitor form a trigger circuit, a power source having a positive terminal connected to the anode side of said discharge tube and said power source having an opposed negative terminal, said means for establishing said series connection between said main capacitor and additional capacitor upon closing of said trigger switch including a resistor connected between said negative terminal of said power source and said trigger circuit and separating said trigger circuit from said negative terminal.

4. The combination of claim 3 and wherein said means for establishing said series connection further includes a second resistor connected between said main capacitor and additional capacitor with said trigger switch being connected to a junction between said main capacitor and second resistor. 

1. In an electronic flash device, a discharge tube having a pair of electrodes, a main capacitor electrically connected between said electrodes for regulating the inter-electrode voltage of said discharge tube, an ignition transformer operatively connected with said discharge tube for bringing the latter into a state of emission, a trigger switch and a trigger capacitor electrically connected with said transformer for actuating the latter to start the emission of said discharge tube, an additional capacitor to be connected by said trigger switch upon closing thereof in series with said main capacitor for providing at an initial period of emission of said discharge tube an interelectrode voltage from said main capacitor and said additional capacitor, and means for establishing said series connection between said main capacitor and additional capacitor upon closing of said trigger switch, said trigger transformer having a primary winding forming a closed-loop series circuit with said trigger capacitor and said trigger switch which thus short-circuits said trigger capacitor across said primary winding upon closing of said trigger switch, said additional capacitor being connected in series with said primary winding with said trigger switch being connected to a junction situated between said additional capacitor and said primary winding.
 2. The combination of claim 1 and wherein said trigger transformer, said trigger switch and said trigger capacitor form a trigger circuit, a power source having a positive terminal electrically connected with the anode of said discharge tube, and said power source having an opposed negative terminal, and said means for establishing said series connection between said main capacitor and additional capacitor including a resistor connected between said trigger circuit and negative terminal of said power source and separating said trigger circuit from said negative terminal.
 3. The combination of claim 1 and wherein said trIgger transformer, trigger switch, and trigger capacitor form a trigger circuit, a power source having a positive terminal connected to the anode side of said discharge tube and said power source having an opposed negative terminal, said means for establishing said series connection between said main capacitor and additional capacitor upon closing of said trigger switch including a resistor connected between said negative terminal of said power source and said trigger circuit and separating said trigger circuit from said negative terminal.
 4. The combination of claim 3 and wherein said means for establishing said series connection further includes a second resistor connected between said main capacitor and additional capacitor with said trigger switch being connected to a junction between said main capacitor and second resistor. 